Dr Michelle Dickinson: nanotechnologist reveals why we crave dessert when we're full

Have you ever finished a huge meal but still found room for dessert? Some people might talk about having a separate stomach for desserts.

It turns out that your brain might be driving you to eat that sweet treat even though you don't 'need' it. 

Recent research in the journal Science found that the same nerve cells that signal 'you’re full' also spark cravings for you wanting something sweet. 

Deep within a part of your brain called the hypothalamus are special cells known as pro-opiomelanocortin (POMC) neurons. They are well known for their role in telling us when we’re full - however, these neurons have been found to have a surprising double life. When sugar enters your mouth, POMC neurons release natural opioids, like ß-endorphin, which trigger a rewarding sensation making us want more of the sugar even if our stomach is already full.  

The researchers found this out using experiments on mice. First, they bathed slices of mouse brain tissue in a fluorescent solution that binds to opioid receptors. They found that the highest density of these receptors was in a brain region known as the PVT, a key player in regulating feeding behaviours. This hinted at a direct link between the fullness signal and sugar cravings.  They then let some lab mice eat their regular meal. After about 90 minutes, when the mice were clearly full, introduced a dessert of sugary food. Neuronal activity between the arcuate nucleus and the PVT spiked to nearly four times the level observed during the meal.  

Interestingly, this surge began before the mice even started eating the dessert, suggesting that the brain anticipates the sweet treat. To confirm this pathway, the scientists used a technique called optogenetics which uses light to control cells. When they inhibited the signals from the POMC neurons to the PVT, the mice consumed 40 percent less dessert. This confirmed that these satiety neurons, far from solely curbing appetite, also drive our desire for sugar when we’re full. 

The researchers hypothesise that this might be evolutionary. Sugar was once a rare and quick source of energy and our brains evolved to seize opportunities when they come around, which may have meant eating more energy rich foods when you’re already full.  

While sugar is now plentiful, that ancient wiring could still make us crave a sweet finish to our meals. 

Understanding that our dessert cravings have a neurological basis might help pave the way for new approaches to combat overeating and obesity. By targeting the specific brain pathways that drive sugar cravings, future treatments could help reduce excessive sugar consumption without dampening overall appetite. 

Next time you’re tempted by that slice of cake after dinner, remember: it’s not just a sweet tooth, it’s your brain’s finely tuned system working as it has for millennia. 

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Episode Transcript

Speaker 1 (00:06):
You're listening to the Sunday Session podcast with Francesca Rudgin
from News Talks.

Speaker 2 (00:11):
It'd be good to have you with us. It is
time for our Science Study the Week, and I'm joined
by doctor Micheldikinson. Good morning, Good morning. This might be
something that I can relate to. Many of us can
the issue that we are discussing here today.

Speaker 3 (00:26):
So many of us call it a dessert stomach. You
know that extra stomach that you have that always has
room for dessert, even though.

Speaker 2 (00:34):
Even when you sort of focus on I'm going to
leave some room for dessert, and you know that you
don't hear room for dessert. You still, yeah, there's always room.
Is that other Yeah, that other stomach that I can
put it in.

Speaker 3 (00:42):
Well, we didn't realize before where this room comes from,
and actually it comes from, thanks to a new study
that's published in the journal Science this week, it comes
from your brain basically tricking you you don't have extra room,
but your brain has set this up for you. So
this beautiful study, which was tested out on mice, has
actually found this new link in a place called your

(01:03):
in your brain called the hypothalamus, and in side there
are these neurons and they're called POMC neurons, which stands
for pro opio milano caught in neurons. Don't worry about
the name of it. Basically, these are the neurons that
tell you when you're full. They tell you to tell
you to stop eating, so your brain goes had too
much to eat. It's sort of the connection between your

(01:24):
stomach and your brain that says, had too much. Stop
eating now, otherwise we would eat forever. It's good that
we have these things.

Speaker 1 (01:29):
Now.

Speaker 3 (01:29):
We've always thought that that's all they did. Well, this
new research has actually found that these neurons release natural
opioids called beta endorphins, which trigger a reward sensation in
your brain when they when sugar enters your mouth. So
when sugar enters your mouth, these POMC neurons that are

(01:50):
usually designed to tell you your fun also release basically
an endorphin that goes, oh, wasn't that nice? Can we
have some more of that please? And we all go, yes,
I'll just eat some more sugary dessert.

Speaker 2 (02:02):
That it can even start before you've put the sugar
in your mouth, like even just thinking about it.

Speaker 3 (02:06):
So what they did is they took these mice and
they basically gave them a massive dinner, and then nineteen
minutes later, they gave them a sugary dessert, and they
studied their brains and these mice went ballistic for this dilute.
And what they found is the neural activity spiked four
times to the level that was drawing their meal in
this POMC neurine area. And then they went, oh, well,

(02:28):
let's study it when we just show them the dessert.
So as they started to bring the dessert out, the
mice's brains were going nuts. I mean that it's not
just the sugar, it's you thinking about the sugar, and
this reward sensation has already gone off that triggers you
to go, I need that sugar. I need that sugar.
And then you have the sugar, and then you get
this lovely release of endorphin in to your I want
more sugar. And what they did is they use this

(02:50):
really cool thing called optogenetics, which is where they can
shine light on the brain of these mice to stop
this pathway from working. So basically, it stops these POMC
neurons from being able to give off this lovely endorphin.
And as soon as they did that, the mice basically
didn't eat their dessert, So it shows that that pathway

(03:10):
is the pathway. And the reason why this is interesting,
other than feeding a whole bunch of mice sugary desserts,
is that now we know that that is why people
are craving sugary things and they're feeling almost an addiction
to it.

Speaker 2 (03:22):
I was going to say, is this proof that you
can be addicted to.

Speaker 3 (03:26):
Sugar hundred percent? Oh, you're addicted. You get a feeling
of pleasure, which is nice. And so they've gone, well, look,
we can look at antiobesity drugs and things that actually
cut this off. Great idea, but I'm just imagining all
these little mice eating all of these desserts, having light
shine at their.

Speaker 2 (03:42):
Brain and it's taken away.

Speaker 3 (03:45):
Well, why does this even happen? So they've actually gone
back and gone well, back in when our ancestors time,
sugar was so scarce that if you came across it,
you should really take it in because you need the
energy to boost your system even if you're full. So
it was designed as an override so that when you
saw sugar, which is very rare, you consume it. So
you don't waste it on more past it. But now

(04:07):
that sugar is abundant, we just we can just blame
all u on, shall we. So don't feel bad if
you've got a dessert stomach. It's an ancestral thing that
has happened through evolution. But no, it's there and if
you want it to and off, you can say no
to that it. You don't have an extra space or
an extra stomach for it. It's just your brain trick
in you. I love it.

Speaker 2 (04:26):
Where do we find the study in the general science? Fantastic?
Thank you so much.

Speaker 1 (04:32):
For more from the Sunday session with Francesca Rudkin, listen
live to News Talks It'd be from nine am Sunday,
or follow the podcast on iHeartRadio.